The absorption, distribution, metabolism and excretion of 14C-labeled 1,2-dihydro-2,2,4-trimethylquinoline (TMQ) was studied in male F344 rats. TMQ was readily absorbed, distributed to all tissues, metabolized and excreted mainly in the urine in the form of several metabolites. The rate of clearance from the tissues is rapid and the whole body half-life is less than 12 hours. Only liver retained significant quantities of TMQ-derived radioactivity 24 hours after an intravenous dose of 115 Mumole/kg body weight. In vitro studies indicated that TMQ is readily metabolized by hepatic mixed-function oxidases and that some of the initial metabolites are conjugated prior to excretion.